function _select(client,selectSQLString)
{
    client.query(selectSQLString,  function selectCb(error, results, fields)
    {
        if (error)
        {
            console.log('GetData Error: ' + error.message),
            client.end();
            return;
        }
        if(results.rowCount > 0)
        {
            var firstResult,
            resultSet = '';
            for(var i = 0, len = results.rowCount; i < len; i++)
            {
                firstResult = results.rows[i];
                resultSet += 'id:' + firstResult['id'] + ' ' + 'name:' + firstResult['name'] + ' ' + 'userName:' + firstResult['username'] + '\n';
            }
        }
        console.log(resultSet);
        /* 添加功能：使查询结果集返回到客户端并保证此函数的通用性. */
    });
}

exports._select = _select;